1. Field of the Invention
The present invention relates to honeycomb structure bodies and methods of designing honeycomb structure bodies
2. Description of the Related Art
There have been known and widely used honeycomb structure bodies used in catalyst converters mounted on exhaust gas purification systems for motor vehicles, capable of purifying exhaust gas emitted from internal combustion engines such as diesel engines. Such a honeycomb structure body is mounted on an Inside of an exhaust gas pipe in an exhaust gas purification system connected to an internal combustion engine in order to purify exhaust gas. In general, a honeycomb structure body has an outer peripheral wall of a cylindrical shape, partition walls arranged in a lattice shape in the inside of the outer peripheral wall. In particular, the partition walls are formed to be arranged in a lattice shape to form a plurality of cells along an axial direction of the honeycomb structure body. That is, each of the cells is surrounded by the partition walls. The cells are formed along an axial direction of the honeycomb structure body, and catalyst is supported in the cells.
Exhaust gas emitted from the Internal combustion engine is discharged outside through the exhaust gas pipe. Because exhaust gas is a high temperature gas, the catalyst supported in the honeycomb structure body is activated by heat energy of the exhaust gas. The honeycomb structure body supporting activated catalyst of a high temperature purifies the exhaust gas when the exhaust gas passes through the cells formed in the honeycomb structure body.
When the honeycomb structure body is divided into two sections, i.e. a central section (as an inner section) and an outer side section viewed on a radial cross section of the honeycomb structure body, there is in general a tendency that a large amount of exhaust gas passes through the cells arranged in the central section of the honeycomb structure body when compared with an amount of exhaust gas passing through the cells arranged in the outer side section of the honeycomb structure body in a radial cross section. Such a radial cross section of the honeycomb structure body is a cross section in a radial direction which is perpendicular to an axial direction or a longitudinal direction of the honeycomb structure body.
For example, a patent document, Japanese patent laid open publication No. 2002-177794 has disclosed a honeycomb structure body having a conventional structure in which a radial cross section of the honeycomb structure body is divided into two sections, i.e. a central section (as an inner section) and an outer side section. In order to improve the purification capability of exhaust gas, an amount of catalyst supported in the central section is increased, and on the other hand, an amount of catalyst supported in the outer side section is decreased.
However, the honeycomb structure body disclosed in the patent document previously described has a drawback as follows. The honeycomb structure body disclosed in the patent document has the central section of the honeycomb structure body in which a large amount of catalyst is supported in the cells of the central section in order to increase the exhaust gas purification capability of the central section as compared with that of the outer side section. However, this structure cannot solve the conventional problem previously described, i.e. cannot eliminate a difference in flow amount between the central section and the outer side section.
When such a difference in flow amount occurs between the central section and the outer side section, the central section becomes a high temperature and the outer side section becomes a low temperature. Accordingly, the outer side section requires a long period of time until a temperature of the cells with catalyst formed in the outer side section reaches the catalyst activation temperature when compared with the central section. Further, there is another possible problem that the cells of the outer side section cannot reach the activation temperature to sufficiently activate the catalyst. This reduces the purification capability of the honeycomb structure body.